1. Field of the Invention
The present invention relates to a current limiting module and a hybrid current limiter using different kinds of superconducting wires. In particular, the present invention relates to a current limiting module and a hybrid current limiter that hardly generate resistance in a normal current state and generate high resistance in a fault current in order to limit current. When large fault current is generated in an electric power system, such as a power transmission line, a motor, and a generator that transmits large current, the current limiting module and the hybrid current limiter may be used to limit current.
2. Description of the Related Art
Superconducting current limiters, which limit large fault current generated in a system, may be generally classified into a resistive superconducting current limiter and an inductive superconducting current limiter. The inductive current limiter generally limits impedance by using an inductance component as impedance, and the resistive current limiter generally limits current by using a resistance component as impedance. Further, a non-inductive winding type current limiter is a resistive current limiter. If fault current exceeds the critical current of the superconducting current limiter, the non-inductive winding type current limiter generates resistance through the phase shift of a superconductor, and limits fault current by using the resistance as impedance. In the related art, a non-inductive winding type current limiter employs HTS (high temperature superconducting) wires. As for the non-inductive winding type current limiter, impedance is zero in a normal current state, impedance is generated after fault, and the impedance is adjusted to zero after the completion of the fault.
Since normal current flows in the non-inductive winding type current limiter during most of time, the impedance of the non-inductive winding type current limiter needs to be minimized. Even when the resistance of the current limiter is zero, the structure in which superconducting lines are wound generates inductance. There are a bifilar winding, a series type non-inductive coil, and a parallel type non-inductive coil as the structure for minimizing the inductance generated as described above. Among them, the parallel type structure includes two wires that are wound adjacent to each other, and has advantages in terms of electrical insulation and thermal stability. A coil having a parallel type structure has small impedance that is caused by an AC component of current in a normal state, and large resistive impedance that is caused by current quench in a fault state. In the parallel type structure in the related art, the magnetic flux generated from two wires has the same intensity and different direction. For this reason, inductance components are offset to each other, and the impedance caused by current in a fault state has only a resistance component.
A superconducting material is a material that causes superconductivity in ranges lower than critical temperature, critical current density, and critical magnetic field. In general, the superconducting material is manufactured in the form of a wire, a thin film, bulk, and the like. In particular, since having zero impedance in a normal state, a superconducting wire is used to transmit large current without loss or to generate ferromagnetism. Since a fault current limiter using the superconducting material should have zero impedance in a normal current state, non-inductive coils may be applied to the fault current limiter.
Korean Patent Publication No. 2001-122194 discloses the following current limiter. In the current limiter, an inner bobbin is provided in an outer bobbin, and the outer bobbin is provided with superconducting modules where wires are wound in opposite directions so as to be connected to each other through current terminals in parallel. Further, the modules are formed by a connecting member so as to be symmetrical with each other in a vertical direction. Since the magnetic fields of the current limiter are offset to each other, the current limiter does not generate an inductance component. Further, since generating only a resistance component depending on the intensity of fault current, the current limiter has a limitation that current cannot be limited by inductance in a fault state.